The present invention relates to a coupling device for a pipe, comprising a sleeve having an insert and for the pipe and sealing means suitable for realizing a seal around the pipe inserted in the sleeve, said sealing means comprising a plurality of mutually slidable elements which together form a ring, and a grip ring being mounted inside said elements and extending along at least a part of the circumference of the pipe.
Such a coupling device is disclosed in the European patent application EP-A-0 794 378, corresponding to U.S. Ser. No. 08/790,146, which has been incorporated by reference herein, and assigned to the present applicant. The coupling device is used for pipes made of steel, stainless steel, eternite, cast-iron, coated steel, PVC, polyethylene and asbestos cement, and is used for coupling two such pipes. It is of importance that on the one hand the coupling device provides an adequate seal and that on the other hand said coupling device is able to withstand tensile strain. This latter function is provided by the grip ring that is part of the coupling device.
From the Dutch patent application 1009734 to applicant, corresponding to U.S. Ser. No. 09/360,983, which has been incorporated by reference herein, a grip ring is known embodied with projections that are pressed out of the surface of the grip ring. At one side the projections then are delimited by slit-like openings punched out of the grip ring. While this grip ring is effective on pipes made of harder material, when using it on pipes that are made of a softer material, it seems to have the effect of a cheese slicer, with the result that the tensile strength of the coupling device is accordingly relatively limited. When such a coupling device is used with such softer materials as polyethylene, polybutene, acryl butadiene styrene, or polypropylene, a tensile strain of approximately 6 to 7 bars may apply in the large diameters, and in the smaller diameters this may be 15 to 16 bars. It would thus be desirable to provide a grip ring permitting higher tensile values.
It is the objective of the invention to provide a grip ring such having improved tensile values. In accordance with the invention, this is achieved by embodying the grip ring with projections that extend substantially radially inwards from the surface of the grip ring. It has been shown that when the coupling device according to the invention is applied to such a pipe made of relatively soft material and having a diameter of 200 mm, for example, it tolerates a tensile strain of 25 to 30 bars, as compared to 6 to 7 bars.
Preferably, the projections are pressed out of the surface of the grip ring and formed such that over a first distance in the circumferential direction of the grip ring said projections have rims delimiting said projections and extending inwardly, while over a second distance, which second distance is smaller than the first distance, having a portion extending inwardly between said rims. This provides a set of substantially symmetrically formed projections with the result that the grip characteristic is invariant with regard to the direction of any possible rotational strain the pipe may exert on the coupling device.
In a further aspect of the invention, the grip ring is equipped with projections having a double wedge shape, the two wedge shaped portions being positioned in each other""s extended direction with their low sides abutting. In accordance with the form thus conferred on the projections, they substantially follow the periphery of the pipe to be clamped, while also providing a relatively large contact surface with which the projections clamp the pipe. The height of the projections necessary may be a mere 1 mm maximally, so that the depth of penetration into the pipe is kept very much to a limit. Moreover, it is a xe2x80x9crestrictedxe2x80x9d penetration; the projections do not make an undesirable radial notch in the pipe.
The clamping action of the coupling device according to the invention is furthered especially by holes provided on the grip rings, said holes in longitudinal direction being delimited on either side by the projections.
The invention is also embodied in a method for the fabrication of a grip ring suitable to be used in a coupling device according to the invention, characterized in that angular holes are punched into a plate, and in that subsequently directly adjacent, at either side of the holes, the rims delimiting the holes are bent, followed by shaping the plate into at least a partial ring form.